<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        body{
            margin: 0;
            padding: 0;
        }
        button{
            margin: 20px;
        }
        .no-margin{
            margin: 0;
        }
        .red{
            color: red;
        }
    </style>
</head>
<body>

    hello world!
    <button class="red">hello</button>

    <script src="tethys.js"></script>
    <script>
        $('button').on('click', function(){

            $('body').css({
                'background-color': 'green'
            }).css('font-size', '22px');

            console.log($('body').css('background-color'));
            
            console.log('hasClass red ' + $(this).hasClass('red'));

            $(this).addClass('no-margin').removeClass('red');

            console.log('hasClass red ' + $(this).hasClass('red'));

            $(this).attr('name', 'hap').attr({
                age: 18
            });

            console.log($(this).attr('name'));
        });
    </script>
</body>
</html>